Tube fitting with separable tube gripping device

ABSTRACT

A tube fitting for a tube end has a female member that cooperates with a male member. A tube gripping device in the form of a gripping ring or ferrule is retained with the female member. Upon a partial pull-up, the tube gripping device separates from the female member.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/522,814, filed on Sep. 14, 2006 for TUBE FITTING WITH SEPARABLE TUBEGRIPPING DEVICE, now U.S. Pat. No. 7,407,196, which is a continuation ofU.S. application Ser. No. 10/467,444, filed Aug. 6, 2003, now U.S. Pat.No. 7,108,288 which claims the benefit of International ApplicationSerial No. PCT/US02/03431, filed Feb. 6, 2002 which claims the benefitof U.S. Provisional patent application Ser. No. 60/266,735 filed on Feb.6, 2001 for TUBE FITTING WITH INTEGRAL NUT AND FERRULE, and Ser. No.60/329,943 filed on Oct. 17, 2002 for TUBE FITTING, the entiredisclosures of which are fully incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The subject invention is generally directed to the art of tube fittings.More particularly, the invention is directed to a flareless tube fittingthat uses a tube gripping element that is initially joined to one of thecoupling elements and separates therefrom during assembly onto a tubeend.

BACKGROUND OF THE INVENTION

Tube fittings are used to join or connect a tube end to another member,whether that other member be another tube end such as through T-fittingsand elbow fittings, for example, or a device that needs to be in fluidcommunication with the tube end, such as for example, a valve. As usedherein the terms “tube” and “tubing” are intended to include but not belimited to pipe as well. Any tube fitting must accomplish two importantfunctions within the pressure, temperature and vibration criteria thatthe tube fitting is designed to meet. First, the tube fitting must gripthe tube end so as to prevent loss of seal or tube blow out. Secondly,the tube fitting must maintain a primary seal against leakage. Therequirement that a tube fitting accomplish these two functions has beenthe driving factor in tube fitting design for decades. A multitude offactors influence the design of a tube fitting to meet a desired gripand seal performance criteria, but basic to any tube fitting design willbe: 1) the characteristics of the tubing that the fitting must workwith, including the material, outside diameter and wall thickness; and2) the tube grip and seal performance level required of the tube fittingfor its intended applications. The goal is to design a tube fitting thatreliably achieves the desired tube grip and seal functions withinwhatever cost constraints are imposed on the product by competingdesigns in the marketplace.

A flareless tube fitting generally refers to a type of tube fitting inwhich the tube end remains substantially tubular, in contrast to aflared tube fitting in which the tube end is outwardly flared over afitting component. Flared tube ends are commonly encountered in use withplastic tubing and plastic tube fittings. The present invention is notprimarily directed to plastic tubing or tube fittings because suchfittings have significantly different challenges and material propertiesthat affect the ability of the fitting to both grip the tube and providean adequate seal. However, some of the aspects of the invention mayapply to non-metal tube fittings, particularly the separable tubegripping element aspect.

Tube fittings that are intended for use with stainless steel and othermetal tubing, for example, are particularly challenging to design inorder to achieve the desired tube grip and seal functions. This arisesfrom the nature of stainless steel which, in terms of typicalcommercially available tubing material, is a very hard material, usuallyon the order of up to 200 Vickers. Stainless steel and other metaltubing is also used for high pressure applications in which the tubingwall thickness is substantial (referred to in the art as “heavy walled”tubing). Heavy wall tubing is difficult to grip because it is not onlyhard but it is also not particularly ductile. Low ductility makes itmore difficult to deform the tubing plastically so as to achieve adesired tube grip.

Tube fittings typically include an assembly of: 1) a tube grippingdevice, often in the form of a ferrule or ferrules, or a grippingring-like structure, and 2) a pull-up mechanism for causing the tubegripping device to be installed on a tube end so as to grip the tube endand provide a seal against leakage. The term “pull-up” simply refers tothe operation of tightening the tube fitting assembly so as to completethe assembly of the fitting onto the tube end with the desired tube gripand seal.

Usually a tube fitting is first assembled in a “finger tight” conditionand then a wrench or other suitable tool is used to tighten or “pull up”the fitting to its final initial and complete assembled condition. Thepull up mechanism most commonly used is a threaded connection of afemale threaded nut component and a male threaded body component, withthe tube gripping device being acted upon by these two components asthey are threaded and tightened together. The body includes a tube endreceiving bore with an angled camming surface at the outer portion ofthat bore. The most commonly used camming surfaces are frusto-conicalsuch that the term “camming angle” refers to the cone angle of thecamming surface relative to the tube end longitudinal axis or outersurface. The tube end is axially inserted into the body bore and extendspast the frusto-conical camming surface. The gripping device is slippedonto the tube end and the nut is partially threaded onto the body to thefinger tight position such that the tube gripping device capturedaxially between the camming surface and the nut. The nut typicallyincludes an inward shoulder that drives the tube gripping device intoengagement with the angled camming surface on the body as the nut andbody components are threadably tightened together. The angled cammingsurface imparts a radial compression to the tube gripping device,forcing the tube gripping device into a gripping engagement with thetube end. The tube gripping device typically is to form a seal againstthe outer surface of the tubing and also against the angled cammingsurface.

The most commonly used tube gripping devices in stainless steel tubefittings today (the most commonly used are ferrule-type tube fittings)achieve tube grip by causing a front or nose portion of the tubegripping device to bite into the tube end outer surface. As used herein,the term “bite” refers to the plastic deformation of the tube grippingdevice into the outer surface of the tube end so as to plasticallydeform and indent the tubing with an almost cutting-like action tocreate a generally radial shoulder or wall at the front end of the tubegripping device. This “bite” thus serves as a strong structural featureto prevent tube blow out at high pressure, particularly for largerdiameter tubing such as ½″ and higher.

Over the years there have been numerous tube fitting designs that do notrely on a “bite” type action, but rather merely radially compress thetube gripping device against the tubing outer surface, some with theeffect of indenting into the tubing without creating a bite. Thesedesigns are not suitable for high pressure stainless steel tubefittings. The most common commercially available stainless steel tubefittings especially for high pressure applications have historicallybeen of two radically distinct designs of the tube grippingdevice-single ferrule tube fittings and two ferrule tube fittings.

A single ferrule tube fitting, as the name implies, uses a singleferrule to accomplish both the tube grip and seal functions. However, itis becoming increasingly recognized that these two functions are at oddswith each other when designing a tube fitting that can meet a desiredtube grip and seal performance criteria. This is because the designcriteria needed to assure that the tube fitting achieves an adequatetube grip usually works against the ability of the single ferrule toalso provide an effective seal. Consequently, although prior art singleferrule fittings can achieve adequate tube grip in some cases, this tubegrip performance comes at the expense of having a less effective seal.One result of this situation is that some single ferrule tube fittingshave been designed with additional components and techniques to achievean adequate seal. Less than optimum seal performance is particularlynoted in single ferrule fittings that attempt to seal against gas, andespecially high pressure gas. Single ferrule tube fittings thus areusually more suited to lower pressure liquid applications such ashydraulics, however, even in such lower pressure applications singleferrule seal performance remains less than desired.

For single ferrule tube fittings, the biting action is usuallyassociated with the single ferrule being designed to bow in a radiallyoutward direction from the tube wall in the central region ormid-portion of the single ferrule body between the front and back endsthereof. The front end of the ferrule is driven against the angledcamming surface of the body by the nut pushing against the back end ofthe ferrule. The bowing action helps direct the front end of the singleferrule into the tube end. The bowing action is also used to cause theback end of the ferrule to likewise engage and grip the tube end. Thisis accomplished usually by provided an angled drive surface on the nutshoulder that engages the back end of the single ferrule so as toradially compress the back end of the ferrule into a gripping action onthe tube end. In some single ferrule designs, the back end of theferrule apparently is intended to bite into the tube end. This back endtube grip is sometimes used with the single ferrule in order to attemptto improve the tube fitting's performance under vibration because theback end grip attempts to isolate down-tube vibration from affecting thefront end tube bite.

The use of a back end tube grip actually works against the effort togrip the tube end at the front end of the single ferrule. Ideally, thesingle ferrule should be completely in three dimensional compressionbetween the nut and the camming surface of the body. Providing a backend grip actually places a counter acting tension to the single ferrulethat works against the front end compression being used to provide thetube grip. Additionally, the outward bowing action tends to work againstthe effort to grip the tube at the front end of the single ferrulebecause, in order to enable the outward bowing action, the singleferrule requires a lessened mass that is adjacent the tube gripping“bite”. The outward bowing action radially displaces ferrule masscentral to the ferrule body away from the tube end. Consequently, anoutwardly bowed single ferrule fitting could be more susceptible toferrule collapse, loss of seal and possibly tube blow out at higherpressures.

In order to achieve an adequate tube grip on stainless steel tubing,single ferrule stainless steel tube fittings have historically used arather shallow camming angle of between ten and twenty degrees. Thisrange of angles is referred to herein as “shallow” only as a term ofconvenience in that the angle is rather small. The shallow canning anglehas been used in single ferrule fittings to obtain a mechanicaladvantage because the shallow angle provides an axially elongatedcamming surface against which to slide and radially compress the singleferrule front end to bite into the tube end outer surface. Hardstainless steel tubing material necessitated this elongated slidingcamming action in order to be able to get the single ferrule to createan adequate bite for tube grip. Over the years, the single ferrule hasbeen through hardened or case hardened so as to be significantly harderthan the stainless steel tubing, however, the shallow camming angle isstill used today in such single ferrule fittings to obtain a mechanicaladvantage from the ferrule sliding along the camming surface to producethe “bite” so as to assure an adequate tube grip. An example of acommercially available single ferrule tube fitting that uses a casehardened ferrule and a shallow camming angle of about twenty degrees isthe CPI fitting line available from Parker-Hannifin Corporation. Anotherexample is the EO fitting line available from Ermeto GmbH that uses athrough hardened single ferrule and a twelve degree camming angle.

In some single ferrule designs, a non-conical camming surface has beentried whereby an attempt is made to simply press the ferrule against theouter surface of the tube end, thereby not creating a bite. The resultin such cases however is a low grip or low pressure only fitting thatare not well suited to stainless steel fittings.

The shallow camming angle and elongated camming surface and axialmovement needed to achieve an adequate tube grip with a single ferrulefitting, however, compromises the ability of the single ferrule toachieve the seal function, especially in extreme environments and forsealing gas. This is because the front end of the single ferruleattempts to make the seal against the axially elongated camming surface.The radially outward bowing action causes a larger portion of the outersurface of the front end of the single ferrule to come into contact withthe camming surface against which it is being driven. The resultnecessarily is a larger seal surface area between the outer surface ofthe single ferrule and the camming surface. This enlarged seal areacauses an unwanted distribution of the sealing force between the singleferrule and the camming surface, and also creates a larger area forsurface imperfections to allow leaks to occur. This is particularly ametal to metal seal issue (as contrasted to non-metal to non-metalseals: for example, in a plastic fitting it is usually desirable toprovide an enlarged seal contact area because the more highly ductileplastic material can better form a seal between the two surfaces.)

Because historically the single ferrule fitting has used a shallowcamming angle to achieve adequate tube grip, the less than optimum sealfunction is either tolerated as a recognized limitation on theapplication of the fitting, or additional features have been designedinto the single ferrule fitting, most notably attempts to include one ormore elastomeric seals with the single ferrule or with which the singleferrule cooperates to provide a better seal with stainless steel tubing.See, for example, U.S. Pat. Nos. 6,073,976 and 5,351,998. U.S. Pat. No.6,073,976 illustrates a typical example of a single “ferrule” (called a“cutting ring” in the patent) fitting that attempts to solve the “seal”issue with added elastomeric seal. The U.S. Pat. No. 5,351,998 describesthe benefits obtained by separating the tube grip and seal functionsinto two separate components.

A commercially available and highly successful two ferrule fitting usedfor tubing is commercially available from Swagelok Company, Solon, Ohioand is described in U.S. Pat. Nos. 6,131,963 and 3,103,373 both of whichare owned in common by the assignee of the present invention, the entiredisclosures of which are fully incorporated herein by reference. In thistwo ferrule fitting, the tube grip and seal functions also areseparately achieved by the use of two ferrules. The forward or frontferrule provides an excellent seal even against gas, and the back orrear ferrule provides an excellent tube grip.

The front ferrule achieves an excellent seal by camming against ashallow camming surface angle such as twenty degrees. This is becausethe front ferrule does riot need to slide excessively on the cammingsurface in order to achieve a tube grip function. Likewise, the frontferrule is not case hardened because the primary purpose of the frontferrule is to seal and is not to bite into the tube end. Thus therelatively “softer” front ferrule achieves an excellent seal,particularly against gas, even though the body conical camming surfacepresents a camming angle of about twenty degrees.

The back ferrule achieves the tube grip function in the above noted twoferrule tube fitting. The back ferrule is case hardened to besubstantially harder than the tube end. The front end of the backferrule cams against a frusto-conical camming surface formed in the backend of the front ferrule. The ostensible angle of this camming surfaceis forty-five degrees, but due to the sliding movement of the frontferrule, the effective camming angle is actually a shallow angle ofabout fifteen to twenty degrees. Although the effective camming anglefor the back ferrule is shallow, the back ferrule is not required toprovide a primary seal (although it can form secondary or backup seals).The back ferrule also does not exhibit the undesired bowing action butrather grips the tube end as a function of a radially inward hingingaction. As used herein, the term “hinging” refers to a controlleddeformation of the ferrule such that a central region or mid-portion ofthe ferrule body undergoes an inwardly radial compression, as distinctlycontrasted to a bowing or radially outward displacement. Thus, theeffective shallow camming angle not only does not compromise the fittingseal capability, it actually substantially enhances the overallperformance of the tube fitting especially for stainless steel tubing.

By using separate ferrules for each to achieve primarily only one of thekey tube fitting functions, the two ferrule tube fitting achievestremendous tube grip and seal functions. This prior art two ferrule tubefitting thus has enjoyed tremendous commercial success especially in theart of stainless steel tubing in part due to its performancecharacteristics such as high pressure rating on the order of 15000 psi,wide temperature rating of cryogenic to 1200° F. and in manyapplications a significant number of remakes (a “remake” refers to theloosening and re-tightening of a fitting after an initial pull-up).

U.S. Pat. No. 3,248,136 illustrates use of a single locking ring asopposed to a ferrule, wherein the locking ring acts against a surfacehaving an angle that appears to be greater than twenty degrees or more,but the ring does not appear to plastically deform into the tubing butrather remains elastic so that the ring is designed to retain itsoriginal shape after pull-up, both of which are features that areunsuitable for stainless steel tube fittings of the type consideredherein. Japanese utility model publication 44-29659 illustrates atightening ring that appears to be intended to have a bowing effect andgrip the tube at the front and back ends. The fitting does not appear tobe applicable to stainless steel tubing as the tube is covered with aresin cover.

Attempts have been made to design tube fittings with a tube grippingelement that separates during pull-up to function as a single elementtube gripping device. Known designs place the breakaway element on themale threaded component. Additionally, the known designs either forcethe tube gripping element against a shallow camming surface angle or donot attempt to create a tube gripping bite into the tube wall. Thus theprior art designs suffer from the same limitations as the prior artsingle ferrule tube fitting designs.

Many applications and uses of the above-described two ferrule SWAGELOKtube fitting do not require such high pressure, temperature and remakeperformance characteristics. The present invention is directed to a newfitting concept that can meet lower performance characteristics withoutcompromising overall fitting integrity and performance.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a new tube fittingconcept requires user assembly of only two components, namely a femalefitting component and a male fitting component. The female fittingcomponent and the male fitting component may be adapted to be threadablycoupled together by relative rotation therebetween. The female fittingincludes an initially retained tube gripping element or ferrule. Thetube gripping element may be machined with the female fitting componentor separately attached thereto by any convenient process such asbrazing, welding or soldering, for example. The ferrule in oneembodiment is designed to have a hinging action and to plastic deformduring pull-up to embed the nose portion into the tubing wall forexcellent tube grip, and an axially adjacent swage or collet zone thatisolates the embedded nose portion from vibration effects. The hingingaction also helps to keep the ferrule outer tapered surface in agenerally line contact with the camming surface.

The ferrule in one embodiment is designed to have a hinging action andto plastic deform during pull-up to embed the nose portion into thetubing wall for excellent tube grip, and an axially adjacent swage orcollet zone that isolates the embedded nose portion from vibrationeffects. The hinging action also helps to keep the ferrule outer taperedsurface in a generally line contact with the camming surface.

These and other aspects and advantages of the present invention will beapparent to those skilled in the art from the following description ofthe preferred embodiments in view of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, preferred embodiments and a method of which will be describedin detail in this specification and illustrated in the accompanyingdrawings which form a part hereof, and wherein:

FIG. 1 illustrates in half longitudinal cross-section an exemplaryembodiment of a tube fitting in accordance with the invention in afinger tight position;

FIG. 1A illustrates an embodiment of the tube fitting shown in FIG. 1where a tube gripping element is separately attached;

FIG. 2 illustrates the embodiment of FIG. 1 in a partially pulled upposition;

FIG. 3 illustrates the embodiment of FIG. 1 in a completed initialpulled up position; and

FIG. 4 illustrates another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance then with one aspect of the invention, a tube fitting isprovided having a tube gripping device that initially is integral withone of the coupling elements and upon pull-up separates therefrom tofunction as a single ferrule fitting. In the preferred embodiment, thetube gripping device or ferrule is integrally formed with a femalethreaded nut and is attached thereto by a frangible thin web portionthat breaks as the ferrule cams initially against a camming surface ofthe male threaded component. As a single ferrule after separation, theferrule acts against the steep camming angle surface of a male threadedbody. The steep camming surface angle is particularly advantageous whenthe hardness of the tube gripping device has a ratio of at least about3.3 times greater and preferably at least 4 times greater to thehardness of the tubing material.

Although a number of aspects of the invention are described herein asbeing incorporated into the exemplary embodiments, such descriptionshould not be construed in a limiting sense. For any particularapplication the various aspects of the invention may be used as requiredin different combinations and sub-combinations thereof. Furthermore,although the present disclosure describes and/or illustrates a number ofdesign choices and alternative embodiments, such descriptions are notintended to be and should not be construed as an exhaustive list of suchchoices and alternatives. Those skilled in the art will readilyappreciate and understand additional alternatives and design choicesthat are within the spirit and scope of the invention as set forth inthe appended claims.

Although the various embodiments are described herein with specificreference to the fitting components being made of stainless steel, andin particular 316 stainless steel, such description is intended to beexemplary in nature and should not be construed in a limiting sense.Those skilled in the art will readily appreciate that the invention maybe realized using any number of different types of metal materials forthe fitting components, as well as metal tubing materials, including butnot limited to 316, 316L, 304, 304L, any austenitic or ferriticstainless steel, any duplex stainless steel, any nickel alloy such asHASTALLOY, INCONEL or MONEL, any precipitation hardened stainless steelsuch as 17-4PH for example, brass, copper alloys, any carbon or lowalloy steel such as 1018 steel for example, and any leaded,re-phosphorized or re-sulphurized steel such as 12L14 steel for example.An important aspect of the choice of materials is that the tube grippingdevice preferably should be case or through hardened to a ratio of atleast about 3.3 and preferably 4 or more times harder than the hardesttubing material that the fitting will be used with. Therefore, the tubegripping device need not be made of the same material as the tubingitself. For example, as will be discussed hereinbelow, the tube grippingdevice may be selected from the stainless steel materials noted above,or other suitable materials that can be case hardened, such asmagnesium, titanium and aluminum, to name some additional examples.Furthermore, the frangible feature of the tube gripping ring and femalethreaded nut may also be realized in non-metal tube fittings.

With reference to FIG. 1, the present invention contemplates a tubefitting 50 in which there are only two discrete components prior toassembly, namely a female threaded nut 52 and a male threaded body 54.The nut 52 is substantially different from the typical nut used in aprior art ferrule type tube fittings. The body 54 may be the similar ingeneral design as a typical body used in prior fittings, however, aswill be explained further herein, it is preferred but not necessary thatthe body 54 also be optimized for proper make-up with the new nut 52.Additionally, the body 54 need not be a discretely separate componentbut may be attached to or otherwise integral to another part such as avalve body, manifold or other components for example.

Note that in the drawings the fittings are illustrated in longitudinalcross-section but only half of the section is illustrated, it beingunderstood that the other half is identical and omitted for clarity andease of illustration. In all of the illustrations herein, various gapsand dimensions are somewhat exaggerated for ease of illustration.

The body 54 is a generally cylindrical main body 56 that has an integralextension or end 56 a. The end extension 56 a may be a hex body, forexample, or part of another component such as for example a valve bodyas noted hereinabove. The main body 56 may be machined from the samestock as the end extension 56 a or may be otherwise attached such as bywelding or other suitable technique. The body 56 includes a firstcentral longitudinal bore 58 that is appropriately sized to closely andslideably receive a tube end 13. The first bore 58 is somewhat larger indiameter than a coaxial second bore 59 that extends through the endextension 56 a of the body 54. Of course, if the fitting 50 is a closedend connection, the inner bore 59 would not be a through bore.

The tube end 13 preferably bottoms against a counterbore 60. The body 56is machined or otherwise formed with external male threads 62 thatthreadably mate with corresponding female threads 64 formed or machinedin the nut 52. It is contemplated that in order to avoid inadvertentmixing of old and new style body and nut parts with prior art fittingcomponents, that the thread pitch on the nut and body of the presentinvention may be substantially different from the thread pitch values ofprior art ferrule-type tube fitting nuts and bodies. This will avoidinterchange problems and also allows for a course pitch that provideshigh axial stroke with reduced nut rotation for complete pull-up. Forexample, a fitting that incorporates the present invention may usecourse pitch threads that provide sufficient axial displacement toachieve proper pull-up in a half turn. A typical prior art fitting bycomparison is pulled-up with 1¼ to 1½ turns. Nothing however preventsthe designer from making the thread pitch any value suitable to aparticular application, as there are other techniques to avoidinterchange issues. Therefore, the one-half turn for pull-up is just oneexample of a variety of design choices available.

The central body bore 58 is preferably although not necessarily formedwith a slight radially inward taper a relative to the longitudinal axisX (FIG. 1) of the tube end 13 such that the diameter of the bore 58decreases radially in the axial direction towards the counterbore 60.For example, this taper may be about 2° to about 4°, although theselected angle is not particularly critical. The bore 58 diameter at thecounterbore shoulder is just slightly less than the outer diameter ofthe tube end 13. In this manner, the tube end 13 has a slight radialinterference fit of a few thousandths of an inch for example with thebore 58. This interference between the bore 58 and the tube end 13provides an anti-rotation action to help prevent the tube end 13 fromrotating during pull-up. This also reduces residual torsion stress thatmay be induced into the tube end due to rotation of the tube grippingelement (80) during pull-up. The tube end 13 does not necessarily haveto bottom completely against the counterbore shoulder 60. This isbecause the interference fit helps provide a good primary seal betweenthe bore 58 and the tube end 13. The interference fit also helps improvethe tube grip by the tube gripping element (80) by axially holding thetube end stationary during pull-up so that the full axial displacementof the tube gripping element (80) is used for proper deformation andtube grip rather than any lost axial motion or movement of the tube endduring tightening. The taper of the bore 58 may extend gradually alongits entire axial length or a shorter axial portion adjacent thecounterbore 60.

The nut 52 includes a first central bore 70 having a first diameter D1relative to the longitudinal axis of the fitting 50. The nut 52 alsoincludes a second bore 72 having a second diameter D2 relative to thecentral longitudinal axis of the fitting 50. In this embodiment, thediameter D2 is less than the diameter D1. Furthermore, the diameter D2is sized so that the bore 72 defines a generally cylindrical wall thatreceives the tube end 13 (FIG. 2). The first bore 70 terminates at alocation that is axially spaced from the nut back end 74 to form atrepan 75, such that the nut 52 includes a radially inwardly extendingcollar 76. The collar 76 is generally defined by the back end wall 74 ofthe nut 52, the smaller diameter bore 72 and the larger diameter bore70.

In accordance with a significant aspect of the invention, the nut 52includes a tube gripping device 80 that extends axially inwardly in asomewhat cantilevered fashion from the collar 76. The tube grippingdevice in this example is in the general form of a gripping ring 80 andincludes an inner bore 82 that defines a substantially cylindrical wallthat closely receives the tube end 13 (FIG. 2). The diameter D3 of thebore 82 may be the same as or different from the diameter of the secondnut bore 72. The cylindrical wall that defines the gripping ring bore 82extends axially from a tapered front or nose portion 84 of the grippingring 80. The nose portion 84 includes an axially tapered outer surface86 that increases in the radial dimension towards the back end of thering 80. The tapered outer surface 86 extends from a generally radialfront end 85 of the gripping device 80. This generally radial front end85 joins to the inner cylindrical bore 82 at a preferably sharp corner87. Alternatively, however, there may be provided a circumferentialrecess or step or notch or other geometry (not shown) in the front endof the ring 80 having a diameter that is somewhat larger than thediameter D3 and axially extending from the front end 85 towards the backend 74 of the nut 52.

The tapered surface 86 joins the front end 85 preferably by a radiusportion 89 and at its axial opposite end by a radius 86 a to a generallycylindrical portion 91, which in turn joins via a radius 93 to thetrepan 75.

It is noted at this point that the various geometry characteristics ofthe tube gripping device 80 (such as, for example, the various recesses,notches, tapered portions, radius portions and so on) are selected so asto effect an appropriate radially inward hinging action as will befurther explained hereinafter. Accordingly, the geometry of a tubegripping device 80 will be determined by the characteristics of thematerial of the tubing such as hardness and the fitting components, thedimensions of the tubing and the required tube grip and seal performanceneeded for a particular application. Therefore, the specific embodimentsillustrated herein are intended to be exemplary in nature and notlimiting as to the geometry of the tube gripping device. The abovereferenced patents for the two ferrule fitting also illustrateadditional geometry variations to facilitate the hinging effect toobtain a desired tube grip.

In accordance with another aspect of the invention, the tube grippingdevice or ferrule 80 is attached to the female threaded nut 52 by a thinfrangible web portion 95. This web portion breaks (as illustrated inFIG. 2) when the ferrule 80 cams initially against a camming surface(88) during pull-up so that the tube gripping device or ferrule becomesa separate piece and functions with the nut and body in effect as asingle ferrule fitting. The tube gripping device or ferrule 80 may beseparately attached as indicated by reference 195 in FIG. 1A by anyconvenient process. The separated ferrule 80 has a back end 150 that isaxially driven by a radially inwardly extending wall 152 of the nut 52that serves as a drive surface for driving the ferrule 80 forwardagainst the camming surface for completing an initial pull-up. Thefrangible web portion 95 is preferably designed so that upon separationof the device 80 from the nut 52, the surface 95 a that is exposed alongthe break line does not interfere with the drive surface 152 of the nutduring further pull-up to complete the assembly. As used herein, theterms “tube gripping device” and “ferrule” or “single ferrule” are usedinterchangeably when referring to the device 80 after separation fromthe nut 52.

The ferrule 80 is machined with the frangible web 95 portion by forminga radial groove 154 that is angled generally toward the inside of thefemale threaded nut 52. This groove 154 forms the back end 150 of theferrule 80 and also the radial wall 152 of the nut that drive theferrule axially against the camming surface after the ferrule 80separates from the nut 52. Preferably but not necessarily the wall 152and the back end 150 are machined at an angle of about 75° degrees or sorelative to the tube bore axis X, although this angle may be differentdepending on the particular application. These surfaces 152 and 150 maybe contoured to reduce galling and torque if so required.

With reference to FIGS. 1, 2 and 3, the tapered nose portion 84initially engages an axially tapered camming surface 88 that forms anopening to the tube bore 58 in the main body 56. The tapered cammingsurface 88 is a surface that joins the bore 58 wall to the back end wall90 of the body 54. This camming surface 88 is characterized by agenerally frusto-conical contour. However, the shape of the surface 88may be selected from other shapes depending on the particular ringdeformation and tube gripping characteristics required for the fitting50 in a specific application.

Upon a completed pull-up, the back end 90 of the body 54 contacts thetrepan 75 which serves as a positive stop against over tightening.Should remakes be desired, the back end 90 may be axially spaced fromthe trepan 75 upon a completed first pull-up. Proper pull-up in thiscase may be verified using a gap gauge or other suitable technique, asis known.

The tube gripping ferrule 80 is shaped to effect several importantfunctions of the fitting 50. The ferrule 80 must, upon proper pull-up,provide a fluid-tight primary seal against the tapered camming surface88. This seal may be a primary outer seal for the tube fitting 50, ormay be in effect a secondary or back-up seal to any seal formed betweenthe tube end 13 and the body 54, for example along the bore wall 58and/or the counterbore 60. The separated ferrule 80 also will form aprimary seal at the location where the ferrule 80 bites into the outersurface of the tube end 13 in the area where the cylindrical bore 82 ofthe ferrule 80 engages the tube end outer surface. Again, this primaryseal may in effect be a back-up or secondary seal to any seal formed bythe tube end 13 against the body 54. In any event, the ferrule 80 mustform primary seals against the camming surface 88 and the outer surfaceof the tube end 13. In addition, the ferrule 80 must adequately grip thetube end 13 so as to maintain seal integrity under pressure, temperatureand vibration effects, and to prevent the tube end from separating fromthe fitting under such circumstances.

In order to achieve a fluid-tight seal and tube gripping action, theferrule 80 is designed to be plastically deformed and swaged into thetube end upon completed pull-up, as illustrated in FIG. 3. This resultis achieved by designing the ferrule 80 to have a hinging action wherebythe tapered nose portion 84 is not only driven axially forward as thenut 52 is threaded onto the body 54, but also is radially displaced ordriven into engagement with the outer surface of the tube end 13 wall.The forward end 92 of the nose portion 84 is thus compressed andembedded into the tubing wall with a resultant stress riser or bite inthe region designated 94 in FIG. 3. The front end bite 94 produces agenerally radially extending wall or shoulder 99 formed out of theplastically deformed tube end material. The shoulder 99 engages theembedded front end 92 of the gripping ring 80 to thus form anexceptionally strong mechanical resistance to tube blow out at higherpressures. The embedded front end 92 thus provides both an excellentseal and a strong grip on the tube end 13. The ring 80 is furtherdesigned to exhibit the aforementioned radially inward hinging action soas to swage or collet the cylindrical wall 82 against the tube end at alocation axially adjacent or spaced from the stress riser bite 94 andgenerally designated with the numeral 96. This swaging and collet effectsubstantially enhances the tube gripping function and serves to isolatethe embedded nose portion and bite 94 from the effects of down tubevibration and also temperature changes.

Although the present invention is described herein in the variousembodiments as effecting an embedded nose portion and attendant swagingaction, those skilled in the art will appreciate that in someapplications such rigorous design criteria may not always be required,particularly for fittings that will be exposed to moderate temperature,vibration and pressure effects. Therefore, the additional design aspectsof the nut, body and gripping ring set forth herein as preferredembodiments should therefore not be construed in a limiting sense butrather as selectable enhancements of the basic concepts of the inventionto be used as required for particular applications.

In order to achieve the desired swaging action and tube grip, theferrule 80 is designed to exhibit the hinging action that allows thetapered nose portion 84 and the central or mid-portion (as at the regionof the cylindrical bore 82 or the region designated 94) of the grippingring 80 to be radially inwardly compressed as it engages with thetapered camming mouth 88 of the body 56. This hinging action is alsoused to provide a significant radial displacement and compression of thecylindrical wall 82 to swage a central or mid-portion of the ferrule 80body onto the tube end 13 axially adjacent to the stress riser 94. Inthe embodiment of FIGS. 1-3, the hinging action is facilitated byproviding a preferred although not required radial inner circumferentialnotch 98 that is axially positioned between the cylindrical portions 72and 82. The notch 98 is suitably shaped to permit the ferrule 80 toplastically deform and collapse in a controlled manner so as to radiallycompress the cylindrical wall 82 against the tube end with the desiredcollet effect. The particular geometry of the gripping ring 80 will thusbe designed so that as the nut 52 is further threaded and tightened ontothe body 54 after the ferrule 80 separates, the ferrule 80 hinges andplastically deforms to grip the tube end and to seal both against thetube end and the tapered camming mouth 88. Standard design proceduressuch as Finite Element Analysis may be used to optimize the geometry ofthe ring 80 based on variable factors such as the tubing material,tubing hardness and wall thickness, and required pressure, temperatureand vibration performance characteristics.

Proper deformation of the ferrule 80 may further be controlled byselecting an appropriate contour for the tapered surface 88. Thissurface engages the tapered nose of the ferrule 80 and therefore will inpart determine the timing and manner of how the ferrule 80 hinges,compresses and plastically deforms to properly embed the nose portion tobite into the tubing and also provide the desired collet or swagingaction. Furthermore, the contour of the camming surface 88 may bedesigned to achieve the desired seal between the ferrule 80 nose portionand the tapered surface 88. This seal is important to the overallperformance of the fitting, as is the seal provided between the ferrule80 and the tube end 13.

The nut 52 with its integral tube gripping ferrule 80 may bemanufactured by standard machining operations, and will typicallyinclude a trepan operation to form the outer contour of the ring 80. Theother features of the nut 52 can be realized as well with knownmachining operations. Preferably but not necessarily the nut 52 includeswrench flats 102 to permit the user to tighten the nut 52 onto the body54. Those skilled in the art will readily appreciate that use of thefitting 50 only requires relative rotation between the nut 52 and thebody 54, such that either component or both may be rotated as requiredduring a pull-up operation.

We have found that it is highly desirable for the camming surface 88 toform a camming angle .theta. of about 35°-60° relative to thelongitudinal axis X of the fitting 50 and tube end 13. More preferablythe angle θ of the camming surface 88 should be 40°-50°, and mostpreferred the angle .theta. should be about 45°. This range of anglesfor the camming surface 88 differs dramatically from commonly used metalferrule-type tube fitting designs. Commonly used tube fittings havecamming surface angles in the range of 10°-25°, which is a substantiallyshallower angle compared to the present invention. The shallower cammingangle is necessary in prior art fittings to have the ferrule slide agreater axial distance along the camming surface. This greater slidingaction permits the tube gripping device to be more gradually radiallydeformed into the tube end to form a gripping action or bite on thetube. This is especially the case for stainless steel tubing. Prior tubefittings that included what might appear to be a steeper camming angleactually either rely on a shallow portion of the camming surface or donot produce a bite in the tubing, thereby limiting the pressureresistance of the fitting. The shallow camming angle of the prior art,however, compromises the ability of a single ferrule to form adependable seal. In sharp contrast, the present invention utilizes asubstantially steeper camming surface angle θ, which permits thegripping ring nose portion 84 in effect to be coined into the cammingsurface 88 without substantial sliding action, thereby forming anexcellent seal.

In the exemplary embodiments herein, the nose portion 84 includes theradius portion 89 that transitions to the outer tapered surface 86. Thisouter surface 86 tapers generally at an angle that is not as steep asthe angle of the camming surface 88. The tapered outer surface 86preferably tapers axially with an increasing radial dimension towardsthe back end of the gripping ring 80. This tapered outer portion 86contacts the camming surface 88 with, in effect, a generally narrow zoneor line contact upon pull-up that has high stress and material coiningto allow the front end of the gripping ring 80 to coin into the cammingsurface 88. Therefore, the term “generally narrow line contact” is notintended to preclude an area of contact between the outer taperedsurface 86 and the camming surface 88, but rather more generally to theconcept of a localized contact zone near or at the innermost extent ofthe camming surface 88 of high stress and material coining between theouter tapered surface 86 and the camming surface 88. By “coin” is simplymeant that the gripping ring 80 achieves a good metal to metal sealbetween the radius portion 89 and the camming surface 88 by forming agenerally narrow circumferential line contact of metal burnished onmetal to effect a gas tight primary seal between the tapered surface 86and the camming surface 88.

It is important to note that the use of a particular camming angle isnot dependent necessarily on the contour of the surface 88. In otherwords, the angle of interest is the angle at which the front end of thegripping ring 80 contacts the camming surface 88 to form a seal thereat.Thus, the camming surface 88 may indeed be made with anon-frusto-conical contour, but the seal is still formed by the frontend of the ferrule 80 contacting a steep angled surface 88. Additionalcompound angles or contours of the camming surface 88 may be used tobetter facilitate the hinging action and tube bite achieved by theferrule 80.

Whether the camming surface 88 is formed as a compound angled surfacewith additional angled portions that are steeper or shallower tofacilitate the hinging action and bite of the gripping ring 80 into thetube end 13, in accordance with this aspect of the invention, thesealing portion of the front end of the gripping ring 80 (in theexemplary embodiments the radius portion 89) forms the primary seal on asteep angled portion of the camming surface 88, preferably a steepangled portion in the range of angle θ of about 35°-60° relative to thelongitudinal axis X of the fitting 50 and tube end 13, more preferablythe angle θ of the camming surface 88 should be 40°-50°, and mostpreferred the angle θ should be about 45 at the location where theprimary seal is to be formed. Preferably although not necessarily thisprimary seal is effected by a generally narrow line contact typeengagement between the front end of the gripping ring 80 and the cammingsurface 88.

The steeper camming surface angle has the additional benefit that thenose or front portion of the tube gripping device 80 may be formed withsubstantially more mass as compared to if the front portion had toengage a shallower camming surface angle as in the prior art singleferrule and gripping ring designs. This added mass, along with thehinging action, tends to position a substantially greater mass ofmaterial at or near the location of the tube bite 94. This significantlystrengthens the tube gripping device in resisting pressure and alsostrengthens the collet effect that isolates the bite from vibration andtemperature effects, as contrasted to prior art single ferrule orgripping ring designs. The hinging action also results in the back endof the tube gripping device (i.e. the end opposite the nose end 84) fromcontacting the tube end, so that the entire tube gripping device is inaxial and radial compression.

In general, for a tube gripping device such as a ferrule to embed into,bite and grip the tube end, the tube gripping device must be harder thanthe tube end. This is especially so for thick wall tubing. The greateraxial movement of a ferrule in a shallow angle camming mouth of theprior art allows a ferrule to embed into a tube even when the ferrule isonly moderately harder than the tube. Under these circumstances if thetube gripping device 80 were only moderately harder than the tube end,the device would be unable to adequately grip the tube for a steep anglecamming surface because of the substantially shorter axial movement ofthe tube gripping device during pull-up caused by the steeper cammingangle. However, in accordance with the present invention, by making thetube gripping device significantly harder than the tubing, a steeperangle camming surface may be used and is effective to cause the tubegripping device to adequately bite into the tube end to grip the tube.

The steeper camming angle θ of the present invention also results in amuch shorter distance of axial displacement of the ferrule 80 duringpull-up. Consequently, the nose portion 84 will need to be radiallydeformed and compressed into the tube end 13 with a much shorter axialdisplacement or sliding movement. In order to achieve the proper tubegrip then, the ferrule 80 is preferably case hardened to a hardness ofat least about 3.3 times harder than the tubing material. For example,if the tubing material is stainless steel, it may exhibit a hardness ofup to about 200 Vickers. Therefore, in accordance with this aspect ofthe invention, when the fitting 50 is used with such hard materials, thetube gripping device should be hardened to a ratio of at least about 3.3times harder than the tubing. More preferred, the tube gripping deviceshould be hardened to a ratio of at least 4 times harder than thetubing. Still further, the entire gripping ring 80 need not be casehardened, but rather only the nose portion 84 may be selectively casehardened.

In accordance with this aspect of the invention, all or part of the nut52 and body 54 may be through hardened or case hardened to increase thetube grip of the fitting 50 when used with harder tubing materials suchas stainless steel. Suitable case hardening processes are fullydescribed in U.S. Pat. Nos. 6,165,597 and 6,093,303 and copending patentapplication Ser. No. 09/494,093 filed on Jan. 28, 2000 for MODIFIED LOWTEMPERATURE CASE HARDENING PROCESS, issued to the assignee of thepresent invention, the entire disclosures of which are fullyincorporated herein by reference. These processes produce a hardness ofthe tube gripping device of about 800 to 1000 Vickers or higher withoutcompromising the corrosion resistance of the fitting. Other casehardening techniques however may be used as required. Case hardening ofthe tube gripping ring 80 allows the ring 80 to adequately grip and sealagainst tubing materials such as stainless steel including duplexstainless steel. The above referenced case hardening patents have anadditional benefit of providing surfaces on the ring 80 that reduce orprevent galling between the ring 80 (which rotates with the nut 52) andthe tubing.

Various lubricants may also be used with the tube gripping ring 80 toreduce galling and residual torsion such as, for example, PTFE greases,and greases containing molybdenum disulphide or tungsten disulphide.

Case hardening techniques typically will result in the entire nut 52 andintegral tube gripping ring 80 to be case hardened. When the casehardening is performed on stainless steel, for example, as in the abovereferenced patents or patent application, an adherent oxide skin isformed. In another embodiment of the invention, a solid lubricant may beapplied to the threads of the stainless steel nuts 52 to reduce frictionand the hence pull-up torque during tightening. Any solid lubricant canbe used for this purpose and many such solid lubricants are well known.A few examples are graphite, molybdenum disulfide, tungsten disulfideand UHMWPE (ultra high molecular weight polyethylene). These lubricantscan be used neat, i.e. not combined with another material, or mixed withanother material such as a resinous carrier or the like. In addition,they can be used in essentially any solid form including powders,granules and pastes.

Solid lubricants of this type are well known commercial products.Examples include Dow Corning® 321 Dry Film Lubricant available from DowCorning Corporation of Midland, Mich. and Slickote® Dry Lube 100available from Trans Chem Coatings, of Monrovia, Calif.

These lubricants can be applied by any standard method such as by hand,by aerosol or air spraying or by automatic equipment. Any coatingthickness can be used which will provide lubricating properties. Solidlubricant thickness exceeding standard class 2 thread clearances areusually not required. If appropriate, the lubricant can also be heatedto enhance its adhesion. For example, some lubricants, especially thosesupplied in a resinous binder, can be heated to effect cure of thebinder. For example, Slickote® Dry Lube 100 can be heated followingmanufacturer's instructions to 300° F. for 1 hour, for example.

In a particular embodiment of the invention, a dry lubricant asdescribed above is used on stainless steel nuts 52 which have beensubjected to low temperature carburization using carbon monoxide as thecarbon source. Stainless steel is stainless because of the thin,coherent chromium oxide film which inherently forms when the steel isexposed to air. Low temperature carburization of stainless steel parts,such as those made from AISI 316 and 316L, stainless steel, usuallyleaves the part surfaces coated with a layer of soot. Before use thissoot is usually removed by washing. When carbon monoxide is used as thecarbon source in low temperature carburization, not only does soot formbut in addition a heavy oxide film also forms. This heavy oxide film isconsiderably different from the coherent chromium oxide film which makesstainless steel stainless in that it is thicker and not coherent.Therefore, this film is also removed before use to uncover the part'scarburized surface.

In accordance with this particular embodiment, this heavy oxide film isnot removed before application of the solid lubricant. Rather, it isleft on the carburized part surfaces, or at least the portions of thecarburized surfaces to be lubricated. In accordance this particularembodiment, it has been found that the naturally porous structure ofthis heavy oxide skin acts as an anchor for binding the lubricant to thepart surfaces. As a result, the lubricant is more adherent than wouldotherwise be the case, and hence is able to withstand repeated fittingremakes (i.e., loosening and re-tightening of the nut) without beingremoved.

FIG. 4 illustrates another embodiment of the invention in which allelements are generally the same as the prior embodiment with onevariation. In the frangible web portion 95, a stress concentrating notch300 is formed therein. In this embodiment the stress concentrating notch300 is formed as a generally tight radius that creates a thinner web ofmaterial 302 to promote a rapid clean break of the ferrule 80 from thenut 52. The break thus occurs as a result of a minimal span of rotationof the nut 52 shortly past finger tight position. The shape of the breakis also less ragged. Other shapes of the notch 300 may be used asrequired including elliptical, triangular and so on for example.

The invention has been described with reference to the preferredembodiment. Clearly, modifications and alterations will occur to othersupon a reading and understanding of this specification. It is intendedto include all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

1. A female fitting component for use in a tube fitting in which thereare only two separate components prior to assembly, wherein the only twoseparate components consist of the female fitting component and anexternally threaded male component, wherein the tube fitting grips andseals a tube when the fitting is tightened, wherein the female fittingcomponent comprises: a female nut having internal female threads; a tubegripping device attached with the female nut; wherein assembling of thefemale fitting component with the male fitting component separates thetube gripping device from the female nut; wherein the tube grippingdevice is configured such that during pull-up a forward end of the tubegripping device produces a tube bite into an outer surface of the tube,and said tube gripping device deforms so that a portion of an interiorwall of said tube gripping device that is adjacent to the tube biteisolates the tube bite from vibration.
 2. The coupling device of claim 1wherein the tube gripping device is integrally formed with the femalecomponent.
 3. The female fitting component of claim 1 the tube grippingdevice is separately attached with the female nut.
 4. The female fittingcomponent of claim 1 wherein the tube gripping device consists of asingle ferrule.
 5. The female fitting component of claim 1 wherein thetube gripping device is attached with the female nut by a metalstructure.
 6. The female fitting component of claim 5 wherein said metalstructure is entirely contained within said female nut.
 7. The femalefitting component of claim 1 wherein the tube gripping device isconfigured such that a back end of the tube gripping device movesradially away from the tube during pull-up.
 8. The female fittingcomponent of claim 1 wherein said portion of the interior wall of thetube gripping device that is adjacent to the tube bite is radiallycompressed against the tube to isolate the tube bite from vibration. 9.A female fitting component adapted to join to a male fitting componentof a tube fitting such that the male fitting component extends into thefemale fitting component and cause a tube gripping device to grip a tubeand seal when assembled, the female fitting component comprising: astructure for attaching the tube gripping device to the female fittingcomponent prior to joining the female fitting component with the malefitting component, wherein the structure for attaching the tube grippingdevice to the female fitting component consists of metal; wherein thetube gripping device is attached to the female fitting component andseparates upon pull-up of the fitting.
 10. The female fitting componentof claim 9 wherein the structure for attaching the tube gripping devicealso attaches the tube gripping device to the female fitting componentwhen the female fitting component and the male fitting component are ina finger tight condition.
 11. The female fitting component of claim 9wherein the tube gripping device is configured such that during pull-upa forward end of the tube gripping device produces a tube bite into anouter surface of the tube, and said tube gripping device deforms so thata portion of an interior wall of said tube gripping device that isadjacent to the tube bite isolates the tube bite from vibration.
 12. Thefemale fitting component of claim 11 wherein said portion of theinterior wall of the tube gripping device that is adjacent to the tubebite is radially compressed against the tube to isolate the tube bitefrom vibration.
 13. The female fitting component of claim 9 wherein thetube gripping device consists of a single ferrule.
 14. The femalefitting component of claim 9 wherein said structure for attaching thetube gripping device to the female fitting component is entirelycontained within said female fitting component.
 15. The female fittingcomponent of claim 9 wherein the tube gripping device is configured suchthat a back end of the tube gripping device moves radially away from thetube during pull-up.
 16. A method of making up a tube fitting comprisingthe steps of: attaching a tube gripping device to a female fittingcomponent having internal threads as a separate unit; assembling theseparate unit with a male fitting component; installing a tube end inthe tube gripping device; pulling-up the fitting to secure the tubegripping device on the tube end such that a forward end of the tubegripping device produces a tube bite into an outer surface of the tubeend, and said tube gripping device deforms so that a portion of aninterior wall of said tube gripping device that is adjacent to the tubebite isolates the tube bite from vibration; wherein the tube grippingdevice separates from the female fitting component upon pull-up of thefitting.
 17. The method of claim 16 wherein the tube gripping device isseparately attached to the female fitting component.
 18. The method ofclaim 16 wherein the tube is a pipe.
 19. The method of claim 16 whereinthe tube gripping device consists of a single ferrule.
 20. The method ofclaim 16 wherein the tube gripping device is attached with the femalefitting component by a metal structure.
 21. The method of claim 20wherein said metal structure is entirely contained within said femalefitting component.
 22. The method of claim 16 wherein the tube grippingdevice is configured such that a back end of the tube gripping devicemoves radially away from the tube during pull-up.
 23. The method ofclaim 16 wherein said portion of the interior wall of the tube grippingdevice that is adjacent to the tube bite is radially compressed againstthe tube to isolate the tube bite from vibration.
 24. A tube fittingcomprising: a female fitting component adapted to receive a tube end; atube gripping device; a male fitting component that can be joined to thefemale fitting component such that the male fitting component extendsinto the female fitting component and cause the tube gripping device togrip the tube and seal when assembled and tightened, such that a backend of the tube gripping device moves radially away from the tube duringpull-up; wherein the tube gripping device is attached with the femalefitting component as a separate unit before the female fitting componentis joined with the male fitting component to form the tube fittingassembly; wherein assembling of the female fitting component with themale fitting component disengages the tube gripping device from thefemale fitting component.
 25. The tube fitting of claim 24 wherein thetube gripping device is separately attached to the female fittingcomponent.
 26. The tube fitting of claim 24 wherein the tube is a pipe.27. The tube fitting of claim 24 wherein the tube gripping device isconfigured such that during pull-up a forward end of the tube grippingdevice produces a tube bite into an outer surface of the tube, and saidtube gripping device deforms so that a portion of an interior wall ofsaid tube gripping device that is adjacent to the tube bite isolates thetube bite from vibration.
 28. The tube fitting of claim 27 wherein saidportion of the interior wall of the tube gripping device that isadjacent to the tube bite is radially compressed against the tube toisolate the tube bite from vibration.
 29. The tube fitting of claim 24wherein the tube gripping device consists of a single ferrule.
 30. Thetube fitting of claim 24 wherein the tube gripping device is attachedwith the female fitting component by a metal structure.
 31. The tubefitting of claim 30 wherein said metal structure is entirely containedwithin said female fitting component.
 32. The coupling device of claim31 wherein said portion of the interior wall of the tube gripping devicethat is adjacent to the tube bite is radially compressed against thetube to isolate the tube bite from vibration.
 33. A coupling device fora fitting that grips and seals a tube when the fitting is tightened, thecoupling device comprising: a female fitting component having internalfemale threads; a tube gripping device consisting of a single ferruleattached together with the female fitting component as a separate unitbefore the female fitting component is joined with a male fittingcomponent to form the fitting; wherein assembling of the female fittingcomponent with the male fitting component separates the tube grippingdevice from the female fitting component.
 34. The coupling device ofclaim 33 wherein the tube gripping device is integrally formed with thefemale component.
 35. The tube fitting of claim 33 wherein the tubegripping device is separately attached to the female component.
 36. Thecoupling device of claim 33 wherein the tube gripping device isconfigured such that during pull-up a forward end of the tube grippingdevice produces a tube bite into an outer surface of the tube, and saidtube gripping device deforms so that a portion of an interior wall ofsaid tube gripping device that is adjacent to the tube bite isolates thetube bite from vibration.
 37. The coupling device of claim 33 whereinthe tube gripping device is attached with the female fitting componentby a metal structure.
 38. The coupling device of claim 37 wherein saidmetal structure is entirely contained within said female nut.
 39. Thecoupling device of claim 37 wherein the tube gripping device isconfigured such that a back end of the tube gripping device movesradially away from the tube during pull-up.